"A college degree used to slot you into a 40-year career. Now it's just an entry-level point to your first job," says Guy Berger, the LinkedIn economist who analyzed the career trajectories of 3 million college graduates.

The biggest job hoppers work in media, entertainment, government and non-profits. Millennials that stay in their position the longest typically work in industries where they make things like autos, manufacturing and oil.

There are a lot of theories about why this job shifting revolution is underway.

Young people have always been more restless than their elders, but there's a growing sense that employers see workers as more disposable too. Numerous CNNMoney readers are worried about job security.

"Employers really are churning through the workforce a little faster," says Berger. "Companies are trying to focus on retaining top talent, not just recruiting top talent."

Millennials want to move up the ranks quickly. One of the fastest ways to do that is to change jobs. A new role often comes with a more elevated title and a substantial pay raise (15% or more versus 1 to 3% by someone staying in their current role).

The Great Recession may have also played a role as college grads struggled to get any job, let alone the job they wanted, although Berger notes that jumping around has been on the rise since the 1990s.